I found it quite accurate from what I have read in detail from the Marth/Lucina forums.
The common strategy in most regards when whiffing grabs/moves is to D-tilt>Dolphin slash given its obvious lower recovery and nearly identical startup (2-3 frame diff?).
If opponents decide to roll behind you should have time to protect yourself with your own roll away or pivot grab. Dancing blade is also viable given your timing, but I believe how fast a character is determine its effectiveness. The backward swing of Down smash is stronger than the front one and can be used as a mix-up if they catch on to your dtilt shenanigans, but of course this is for a hard read (Lucina's feet hitboxs too stronk).
If you don't mind a little(alot) of reading you can skim/read through EternalFlame's guide. If you want to get into the gritty frame work behind each move @
Shaya
has work scattered throughout the forums, but I'm sure will be unified at a later time.
http://smashboards.com/threads/marth-combos-setups-strategies.372527/#post-17989567
Also I mentioned this in your stream when you were live that to never counter when being trumped as it will propel you into the blastzone (unknown if fixed in wiiu version).